1. Field of the Invention
This invention relates to a circuit breaker and more particularly to an operating mechanism for a circuit breaker wherein a rotating spring is used as an energy source.
2. Description of the Related Art
Among circuit breakers which use rotational torque output mechanisms as their operating mechanisms, there are some which use a compression coil spring such as disclosed in Laid-Open Patent Heisei 5-54762. However, a variety of studies have been promoted to design better compactization and higher reliability.
A circuit breaker is used for protecting a power system by opening and closing the contacts provided in the circuit breaker. FIG. 8 shows a cross section of a typical vacuum circuit breaker 100. In FIG. 8, a spring mechanism (not shown) is provided in an operating mechanism unit 102 mounted on a frame 105 of vacuum circuit breaker 100 as one of the energy sources for opening and closing the contacts 103, in a breaker unit 101. Operating mechanism unit 102 generates a driving force to open and close contacts 103, 104. Besides, it is required for operating mechanism unit 102 to function to display the opening/closing state of contacts 103, 104, the discharge/charge state of the spring mechanism and so on. Charging the spring mechanism is usually executed by an electric motor (not shown) in operating mechanism unit 102. Operating mechanism unit 102 is also provided with a mechanism (not shown) for charging the spring mechanism manually.
Usually, a compression coil spring or a tension coil spring is used as the spring mechanism in operating mechanism unit 102. In this case, it is required to provide two springs separately for closing and opening contacts 103, 104 in operating mechanism unit 102, and this results in complex construction. In the case that a rotating spring is used as the spring mechanism for the energy source, only one rotating spring is required for both closing and opening contacts 103, 104 in operating mechanism unit 102, and this results in simple and compact construction.
Accordingly, a rotating spring has been used for the energy source in an operating mechanism of a circuit breaker.
Next, control of an electric motor for charging a rotating spring in connection with the opening/closing operation of the contacts is described with reference to FIG. 9. Generally, a circuit breaker is required to provide with the function to "open--close--open" the contacts. This is because a circuit breaker is usually operated to "open--close" the contacts, but it is necessary to "open" the contacts immediately when a fault takes place in a power system at the time of closing the contacts.
In the normal opening--closing operation of the circuit breaker, the energy generated by a rotation of the rotating spring is used for opening--closing the contacts. After the closing the contacts, a limit switch is operated to start operation of the electric motor so as to charge the rotating spring. After that, when the energy sufficient to open--close the contacts is charged again in the rotating spring, the limit switch is opened thereby the electric motor is stopped.
Hereinafter, a typical example of such a circuit breaker which uses a rotating spring, such as a spiral spring or a torsion spring in an operating mechanism is described in detail with reference to the drawings.
FIG. 10 is an enlargement of the essential parts of an operating mechanism of a circuit breaker which uses a rotating spring. In FIG. 10, (a) shows an enlarged front elevation of the essential parts and (b) shows a section, taken along lines A--A and in the direction of the arrow A in FIG. 10(a). In FIG. 10, the outer end of a rotating spring 21 which is an energy source is secured to a spring case 20, and the inner end of rotating spring 21 is secured to a spring shaft 22 which transmits the force. Also, a disc 23 is secured on spring shaft 22. Rail 23a which makes sliding contact with a peg 24 is positioned on the inner face of disc 23, and peg 24 controls release/store control lever 25. Parallel Guides 20a provided in the radial direction of spring case 20 are positioned on an end-plate disc 20b of spring case 20 so that peg 24 can move along parallel guides 20a.
The following is a description of the operation of the circuit breaker shown in FIG. 10, using FIG. 11. Peg 24 engages with rail 23a, and performs a translational motion in parallel guides 20a due to the rotational motion of disc 23 and rail 23a in the B direction.
In the case of opening and closing operation of the circuit breaker, spring shaft 22 rotates in the B direction under the control of a catch which is not illustrated. Contacts in a breaker unit (not shown) of the circuit breaker are opened and closed through a force transmission mechanism (not shown) by the rotation of spring shaft 22 as is well known to those skilled in the art. The opening operation is completed in FIGS. 11(a).fwdarw.11(b), and the closing operation is completed in FIGS. 11(b).fwdarw.11(c).
At the end of the opening and closing operation as shown in FIG. 11(c), the leading end of peg 24 is on the same plane as the outer peripheral surface of end-plate disc 20b. The switching of a microswitch (not illustrated) is performed by pushing up release/store control lever 25 which is supported by a pin 26 so that it is free to rotate. This microswitch is provided for switching ON or OFF a spring energy storing motor.
Due to the switching of the microswitch (not illustrated), rotating spring 21 which has become in the energy-released state, starts to store energy through spring case 20 being rotated in the C direction by a spring energy storing motor (not illustrated).
During the rotation of spring case 20, release/store control lever 25 makes sliding contact on end-plate disc 20b. At the same time, peg 24 performs a rotating motion in the C direction together with spring case 20. Thus peg 24 moves toward the center of spring shaft 22 along rail 23a.
At the end of the energy storing of rotating spring 21 as shown in FIG. 11(a), peg 24 is positioned at Eo, and release/store control lever 25 is in contact with parallel guides 20a.
The detail of the operating mechanism of the circuit breaker as described above is disclosed in French Patent No. 88-10943 published on Aug. 17, 1988.
Control of the microswitch, which is the switch for the spring energy storing motor (not illustrated), is performed by using the motions of release/store control lever 25 due to this series of actions.
However, in this type of circuit breaker, there is a position in which sliding contact is made. Therefore, wear of parts though frequent actions is unavoidable. Consequently, inspection and maintenance, such as greasing, becomes vital, and reliability is reduced.
Also, the number of parts in the operating mechanism is large and this results in complex construction.